Re: Slow I/O on USB media

[Andrea Vai <andrea.vai@unipv.it>]

Il giorno mer, 05/06/2019 alle 19.39 +0200, Greg KH ha scritto:
> On Wed, Jun 05, 2019 at 06:23:58PM +0200, Andrea Vai wrote:
> > Hi,
> > Il giorno mer, 05/06/2019 alle 16.55 +0200, Greg KH ha scritto:
> > > On Wed, Jun 05, 2019 at 09:36:04AM +0200, Andrea Vai wrote:
> > > > Hi,
> > > > Il giorno mar, 04/06/2019 alle 07.43 +0200, Greg KH ha
> scritto:
> > > > > On Mon, Jun 03, 2019 at 01:13:48PM +0200, Andrea Vai wrote:
> > > > > > Il giorno gio, 30/05/2019 alle 06.25 -0700, Greg KH ha
> > > scritto:
> > > > > > > [...]
> > > > > > Hi,
> > > > > > 
> > > > > > > Any chance you can use 'git bisect' to find the
> offending
> > > > > commit?
> > > > > > Yes, I am doing it as I managed to build the kernel from
> > > source
> > > > > 
> > > > > Great!  What did you find?
> > > > 
> > > > # first bad commit: [534903d60376b4989b76ec445630aa10f2bc3043]
> > > > drm/atomic: Use explicit old crtc state in
> > > > drm_atomic_add_affected_planes()
> > > > 
> > > > By the way, as I am not expert, is there a way to double-check
> > > that I
> > > > bisected correctly? (such as, e.g., test with the version
> before
> > > this
> > > > one, and then with this commit applied?)
> > > 
> > > How exactly are you "testing" this?
> > > 
> > > I would recommend a script that does something like:
> > >       mount the disk somewhere
> > >       copy a big file to it
> > >       unmount the disk
> > > 
> > > testing how long the whole process takes, especially the
> 'unmount'
> > > is
> > > important.  Are you doing that?
> > 
> > Well, not exactly, and thank you for pointing me out. I am doing
> the
> > job in two ways, from the DE (when I am located at the PC), or in
> an
> > ssh session when I am away. In ssh I manually mount the media,
> then
> > run
> > 
> > touch begin
> > date
> > <cp command>
> > date
> > touch end
> 
> That tests nothing other than the size of the memory in your system
> :(
> 
> You have to flush the data out to the device fully in order to
> properly
> measure device throughput.  Calling 'touch' does not do that.
> 
> > If I use the DE (where the media is mounted automatically) I used
> to
> > "eject" the media after the copy finished, and took note of the
> time
> > used until the media was correctly "ejected" (and, so, unmounted).
> 
> eject/unmount is good.
> 
> > Anyway, I know that I can do all of this in a better way, and will
> let
> > you know.
> 
> Yes, please do so, your steps above do not show much.
> 
> 

excuse me, another question: since I get the good behavior with kernel
4.20.13 (installed from my distro packages), is it correct to run at
first

git bisect start
git bisect good v4.20.13

, then build the latest kernel, test it, set it as bad (as far as I
can expect) and go on with following tests?

Many thanks,
Andrea